In IBM Technical Disclosure Bulletin, Vol. 26 No. 1, June 1983, page 67-68, a cartridge is described that is attached to a carrier and that is tiltable around an axis parallel to the print line. A reversible drive is shown which in one direction is coupled with the ribbon take-up spool to feed ribbon from the supply spool to the take-up spool, and which if driven in the other direction is used to lift the cartridge to achieve print line visibility by tilting the cartridge about its pivot axis for an appropriate angle. In this known arrangement the cartridge is not coupled directly to the drive means but is installed on top of a plate that is tiltable around an axis and that connects to the drive for ribbon drive, ribbon lift oscillation and print line visibility. The specific interconnection coupling between the ribbon drive incorporated into the cartridge and the reversible ribbon feed device ending on said cartridge plate is not shown.
There are different shapes and forms of couplings, male and female parts, that cooperate with each other yet are still easily detachable.
One form is, for example, shown in U.S. Pat. Nos. 4,091,913 and 4,307,969, both depicting a ribbon cartridge with a crosshole opening on the driven ribbon spool side and a mating blade-like part as extension of the driving axle, sometimes called drive key, on the side of the ribbon feed device. Another form is shown in U.S. Pat. No. 4,231,667 depicting a ribbon cartridge drive with a tooth wheel or gear on the driving side and an adapted mating opening on the hub of the driven ribbon spool. Those known coupling designs normally provide no simple and immediate fitting and no automatic self-centering or self-coupling interconnection. In most cases in a separate action the operator has rotationally to adjust the parts such that driving and driven parts slide into each other for forming the completed coupling.
The normal attempt is to have the engaging parts of the driving ribbon feed device and the driven drive means of the cartridge arranged such that they corotate around the very same axis.
The cross-referenced copending application of Halter et al entitled "Ribbon Drive Coupling and Cartridge Tilt Arrangement for Print Line Visibility" describes a ribbon cartridge which is installed along an axis, about which it is free to pivot within certain limits. This allows the cartridge to drop when print line or writing line visibility is required. This tilting axis is slightly forward of the center of mass of the cartridge, thus, the position of the cartridge is established by the two mounting points arranged on the tilting axis and by a downstop which supports the rear of the cartridge. The downstop is provided by the driving rotating ribbon drive blades on the carrier which engage the ribbon advance knob of the cartridge at the rear of it.
As the drive blades turn, the cartridge knob is forced to turn, which feeds ribbon from the supply to the take-up end. If the blades and the cartridge knob are turning on precisely the same axis, the cartridge will remain stable. However, as intensive experiences have shown, if the two axes of rotation are not coincident, only one of the two drive blades will be engaged at any given time, thus leaving a gap between the other drive blade and its corresponding drive knob surface. This means that only one blade is driving the knob, and this produces an unbalanced force, resulting in a moment about the cartridge tilting axis. As the blades and the knob turn for a complete circle through 360.degree., the magnitude and direction of the force vary, which causes an undesired wobble of the ribbon cartridge and results in a vertical up and down movement of the ribbon in front of the print line. This wobble is not only disconcerting but can result in clipped characters due to unstable ribbon position. Because of tolerances in the parts, there will almost always be some misalignment between the knob and blades and hence a dissatisfying possibility of cartridge wobbling.